1. Field of the Invention
The present invention relates to a method for forming a silicon oxide coating film on a surface of a semiconductor wafer, a glass substrate or the like by SOG (Spin On Glass)
2. Description of Prior Art
As a substrate circuit becomes precise, highly-integrated and multi-layered, there has been performed a method for forming an SiO2 film on a surface of a substrate by SOG (Spin On Glass) for the purpose of insulation between layers and flattening. In order to manufacture a circuit, an interlayer insulating film (hereinafter referred to as “SOG film”) made of SiO2 is formed on a substrate by SOG or the like, a patterned resist mask is provided on the interlayer insulating film, and wiring gutters are formed by performing selective etching and removing the resist mask. After barrier metal is deposited, the wiring gutters are filled with a metal material for wiring such as Cu by electrolytic plating or the like so as to form the lower layer wiring. Next, after the barrier metal and the metal material are polished by CMP (chemical polishing), another SOG film is formed. In the same manner as mentioned above, the SOG film is etched selectively through the patterned resist mask, and via-holes and trench holes (gutters for upper layer wiring) are formed in the SOG film. After barrier metal is deposited on the walls of the via-holes and the gutters for the upper layer wiring, the via-holes and the gutters for the upper layer wiring are filled with a metal material for wiring such as Cu by electrolytic plating or the like so as to form the upper layer wiring.
A method for forming a SOG film has been disclosed, for example, in Patent Document 1. According to this method, a coating liquid made of a solution of an organic solvent containing an acid hydrolysate of trialkoxysilane is applied on a substrate and dried to form a coating film, a surface of the coating film is irradiated with UV in an oxidizing atmosphere, and the coating liquid is further applied. This operation is repeated once or more so as to obtain a desired film thickness. The coating film undergoes heat treatment at 350-500° C. in an inert atmosphere to form a silica-based film having a thickness of 2000 Å or more.
A similar method for forming a SOG film has been disclosed in Patent Document 2. According to this method, a wiring layer made of a material having a melting point of 500° C. or more is provided on a substrate, a coating liquid made of a solution of an organic solvent containing an acid hydrolysate of trialkoxysilane is applied on the wiring layer and dried, and then baking is performed at a temperature of 550-800° C. until no Si—H bond can be observed in the coating film. In this way, an SiO2 coating film having high crack resistance is formed.
Patent document 1: Japanese Patent Application Publication No. 10-310872
Patent document 2: Japanese Patent Application Publication No. 10-313002
The above-mentioned coating liquid containing an alkoxysilane compound also contains an organic solvent. When it is heated, alcohol is generated while the alkoxysilane compound is hydrolyzed so as to form silanol, and water is generated while the silanol undergoes condensation so as to form mesh-like bonds of SiO2. Accordingly, if appropriate drying aroma treatment and baking treatment are not performed, shrinkage of the SOG film occurs, which might cause cracks. Also, in a case where a glass forming material is added to improve crack resistance, when it is heated at a temperature of 500° C. or more, the glass material disappears.
In the technique disclosed in Patent Document 1, only a surface of the coating film is irradiated with UV, and thereby Si—H of trialkoxysilane in the surface of the coating film is converted into Si—OH. With this, it is possible to improve adhesion to another coating film to be formed next so as to prevent pin holes from being generated. However, in this technique, a UV radiation device needs to be installed in a spin coater.
The technique disclosed in Patent Document 2 requires a process for converting Si—H of trialkoxysilane into Si—OH by baking the SiO2 coating film at a temperature of 500° C. or more, preferably 550-800° C. Consequently, the above-mentioned glass forming material cannot be added. There is also a drawback that patterns are destroyed by melting in the case where the material for the wiring layer is metal with a low melting point, such as aluminum.
The object of the present invention is to provide a method for forming a coating film in which the coating film is prevented from drastically shrinking by controlling the temperature accurately when a SOG film is formed in a substrate with a coating liquid containing an alkoxysilane compound, cracks are prevented from occurring in the SOG film by preventing the glass forming material from disappearing, and also metal material of a circuit is prevented from melting and deforming.